How is rayon made?
Since rayon is a regenerated fiber the raw material is obtained from the natural sources that are cotton linters (these are the remnant fibers procured during the ginning process) and wood pulp extracted from pine, spruce or hemlock trees.
The steps involved in the manufacturing of rayon are as follows:
• Pretreatment of Cellulose: The principle behind this step is to soften the lignin content that is present in cellulose without damaging its structure. In order to achieve this purpose, the raw materials are first treated with calcium bisulphite after which boiling with steam under pressure.
• Pressing: The pulp obtained is then made into a thin cellulosic sheet by removing excess liquid by pressing them between a set of two rollers. These sheets have pure cellulose content of about 90-94%.
• Steeping: The cellulosic sheets are then steeped in an alkaline solution of caustic soda which converts them into alkali cellulose sheets.
• Shredding: The alkali cellulose sheets are then dried and shredded into a crumb form referred to as ‘white crumb’ using a shredder machine.
• Ageing and Xanthation: This step involves ageing the crumbs in a metal container while the temperature and humidity must be maintained. The process of ageing takes about 2-3 days followed by the process of xanthation in which the crumbs are churned in carbon disulphide which results in the formation of sodium cellulose xanthate that is bright orange in colour.
• Ripening: The crumbs are then dissolved in sodium chloride and filtered and aged till the right viscosity for about 4-5days.
• Filtration and extrusion: This viscous solution is then filtered to remove impurities and any air bubbles that may be present. This followed by wet spinning i.e. the solution is passed through a spinneret (sieve-like device) that produces long filaments.
• The filament thus obtained are spun into yarns and later into the fabric.